<template>
   <div class="upload-excel">
      <div class="btn-upload">
         <el-button
            :loading="loading"
            size="mini"
            type="primary"
            @click="handleUpload"
         >
            点击上传
         </el-button>
      </div>

      <input
         ref="excel-upload-input"
         class="excel-upload-input"
         type="file"
         accept=".xlsx, .xls"
         @change="handleClick"
      />
      <div
         class="drop"
         @drop="handleDrop"
         @dragover="handleDragover"
         @dragenter="handleDragover"
      >
         <i class="el-icon-upload" />
         <span>将文件拖到此处</span>
      </div>
   </div>
</template>

<script>
import XLSX from 'xlsx'

export default {
   props: {
      beforeUpload: Function, // eslint-disable-line
      onSuccess: Function // eslint-disable-line
   },
   data() {
      return {
         loading: false,
         excelData: {
            header: null,
            results: null
         }
      }
   },
   methods: {
      generateData({ header, results }) {
         this.excelData.header = header
         this.excelData.results = results
         this.onSuccess && this.onSuccess(this.excelData)
      },
      handleDrop(e) {
         e.stopPropagation()
         e.preventDefault()
         if (this.loading) return
         const files = e.dataTransfer.files
         if (files.length !== 1) {
            this.$message.error('Only support uploading one file!')
            return
         }
         const rawFile = files[0] // only use files[0]

         if (!this.isExcel(rawFile)) {
            this.$message.error(
               'Only supports upload .xlsx, .xls, .csv suffix files'
            )
            return false
         }
         this.upload(rawFile)
         e.stopPropagation()
         e.preventDefault()
      },
      handleDragover(e) {
         e.stopPropagation()
         e.preventDefault()
         e.dataTransfer.dropEffect = 'copy'
      },
      handleUpload() {
         this.$refs['excel-upload-input'].click()
      },
      handleClick(e) {
         const files = e.target.files
         const rawFile = files[0] // only use files[0]
         if (!rawFile) return
         this.upload(rawFile)
      },
      upload(rawFile) {
         this.$refs['excel-upload-input'].value = null // fix can't select the same excel

         if (!this.beforeUpload) {
            this.readerData(rawFile)
            return
         }
         const before = this.beforeUpload(rawFile)
         if (before) {
            this.readerData(rawFile)
         }
      },
      readerData(rawFile) {
         this.loading = true
         return new Promise((resolve, reject) => {
            // new FileReader js读取文件的对象
            const reader = new FileReader()
            reader.onload = e => {
               const data = e.target.result
               const workbook = XLSX.read(data, { type: 'array' })
               const firstSheetName = workbook.SheetNames[0]
               const worksheet = workbook.Sheets[firstSheetName]
               const header = this.getHeaderRow(worksheet)
               const results = XLSX.utils.sheet_to_json(worksheet)
               this.generateData({ header, results })
               this.loading = false
               resolve()
            }
            reader.readAsArrayBuffer(rawFile)
         })
      },
      getHeaderRow(sheet) {
         const headers = []
         const range = XLSX.utils.decode_range(sheet['!ref'])
         let C
         const R = range.s.r
         /* start in the first row */
         for (C = range.s.c; C <= range.e.c; ++C) {
            /* walk every column in the range */
            const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })]
            /* find the cell in the first row */
            let hdr = 'UNKNOWN ' + C // <-- replace with your desired default
            if (cell && cell.t) hdr = XLSX.utils.format_cell(cell)
            headers.push(hdr)
         }
         return headers
      },
      isExcel(file) {
         return /\.(xlsx|xls|csv)$/.test(file.name)
      }
   }
}
</script>

<style scoped lang="scss">
.upload-excel {
   display: flex;
   justify-content: center;
   margin-top: 100px;
   .excel-upload-input {
      display: none;
      z-index: -9999;
   }
   .btn-upload,
   .drop {
      border: 1px dashed #bbb;
      width: 350px;
      height: 160px;
      text-align: center;
      line-height: 160px;
   }
   .drop {
      line-height: 80px;
      color: #bbb;
      i {
         font-size: 60px;
         display: block;
      }
   }
}
</style>
